Optical objective.



OR 696978 A) Patented Apr. I, |902.

i ,A C. C. ALLEN.

.1J-f OPTICAL OBJECTIVE.

. (Appnmian mea nu as, 1901.)

(I6 Model.) v2 Sheets-Sheet I.

MH X 20W srrm @u 7@ A www UNITED STATES PATENT OEEICE.

cLILE o; ALLEN, or oIIIcAeo, ILLINOIS.

OPTICAL OBJECTIVE.

SPECIFICATION forming' part 0f Letters Patent N0.A696,788, dated. April 1, 1902'.

Application led February 25, 1901. Serial No. 48,726. (No model.)

To all wiz/om, it may concern.-

Beit known that I, CLILE C. ALLEN, a citizen of the United States, residing at Chicago, in the county of Cook and State of Illinois,

have. invented certain new kand usefull Improvements inOptical Objectives,of which' o t e ens em, an o provide, furtier jhm-W eormeby the objective sha1 zo remain a a xe distance w1 re ere g and the invention consists in an ob- Qective'or lens system composed of three .lens elements, the IiI t and third of which are per- 5 manently fixed-i. Y the front and rear end of the lens-tube, respectively, while the second is movable and capable of being placed in any intermediate position between the first and third elements; and the invention further 3o consists in the-features of construction and combinations of parts hereinafter described and claimed.

In the accompanying drawings, Figure l is a central longitudinal section showing a con- 3 5 `struction of lens-tube and an arrangement of the elements constituting the objective by which a display will be made of the minimum magnitude of the image. Fig. 2 is a similar viewV to Fig. l, showing the position of the 4o elements by which a display will be made of the maximum magnitude of the image; Fig. 3, a cross-section on.line.3 of- Fig. l; Fig. 4, a central longitudinal section ofthe inner carrying-tube and the sliding sleeve or cell carrying' the intermediate element; Figs. 5,

6, 7, and 8,'outline views showing arrangements of the elements on different plans from that shown in Fig. l, but involving the same principle and 'producing the same result. 5o In thedrawings, Figs.- 1,'. 2, 3, and 4 showl a constructipnfof lens-tube adapted to carry the elements in their relative relation to each .other for attaining the end`sought.` The lenstube, as shown, consists of an outer band or support A, screw-threaded onto which isa plate A' for attachment of the tube as awhole to a lantern or other appliance Where the tube, Y

with the elements of the invention located, arranged, and operating therein, is to be used.. v

An outer tube B slides in the band or support' 6o A, and an inner tube C, movable with the outerA tube, is arranged therein, as usual. Alens cell l-. or holder D is screw-threaded into the end ofl the inner tube, and a lens cell' or holder E is v j Y screw-threaded into the end of the inner tube: 6 5" at the opposite end thereof to the lens-holder D. The lens cells or holders carry'kthe fixed. f

elements constituting part of the invention. A sliding cell or support E is located and slides within the interior tube O, and this cell`or sup-M 7o port carries the movable element which' enters into the invention. The cell or support F has, u on its-exteriora roller a, carried by a stud, or

pin a', and this roller projects through.- ai' straight longitudinal slot b in the body ofthe 7 51,

tube C and enters a spiral guideway or track c, between two guide st; ps or railsd, located on the, inner face of andA extending spirallyy from end to end of the tube B, so that by turning or revolving the inner tube the roller 8o A will travel in the track or guideway therefor and advance and recede the cell or support F to locate the element carried thereby adja-4 cent to the elements carried by the lens cells or supports D and E, according as to which end of the lens-tube the cell or-support is adjusted. The lens-tube as a whole-that is, Y the outer and inner tubes 4B 'and C andthe parts carried thereby-is movable in the band or support Aby a spindle G, carrying a pin-'9o ion g, which meshes with a rack fon. the tubes, as shown in Figs.. l, 2, and 3, so that by turning the spindle in one'direction or the other the lens-tube asa whole will be moved 'j forward and back in its band or support. The holder or cell F is held in a direct line of Y travel and maintained in aparallelism of 1 -travel by-a springe, which forces' the opposite side snugly against the interior tube, thereby preventing any end tippingor tilting roo of the holder or cell lin its travel forward and back within the interior tube.

The front element H is carried by the vend cellor ring E, the intermediate adjustable vana-M6" element H is carried by the slidiugholder or cell F, and the rear element H2 is carried by the'cell or ring D by means'of a band D, screw-threaded onto the cell orring and having secured therein the element, as shown in Figs. 1 and 2, and it will be seen that by turn-v ing the tube C in one direction the intermediate element will be carried so as t0 be, in juxtarelation to the front element, as shown in Fig. 1, and by turning the tube C in the other direction the intermediate element will be carried into a juxta relation or position to the element H2, as shown in Fig. 2, and these two points of adjustment give the extremes of display from the maximum to the minimum, and an adjustment between these two points gives a display intermediate of the maximum and minimum points.

The preferred form of the system is shown in Fig. 1 and Fig. 2. The front element H is of the positive or converging type and is of comparatively long focal length. The element H is of the negative or diverging type, being approximately half the focal length of the element H, the rear element H2 being of the positive type and of approximately half the focal length of the element H', the distance between the elements H and H2 being approximately equal to the focal length of the element H2. The elements H and H are constructed of crown-glass of the refractive index of L52 and having the same dispersion, while the element H2 is constructed of two nearly plano-convex cemented doublets, each beingcomposed of a biconvex-crown lens having a refractive index of 1.52, cemented to a nearly plano-concave iint lens having a re fractive index of 1.62, the radii of curvature of the cemented or contact surface being so proportioned as to slightly undereorrect the element as a whole in order to properly compc nsate for the negative aberration of the elements H and H when these elements are placed in juxtaposition one to the other at the front end of the lens-tube, as shown in Fig. 1. The positive aberration of the element H2 is not great enough,however, to counteract the negative aberration vof the element H', so that when the elements H' and H2 are placed in juxtaposition yone to the other, as shown in Fig. 2, their combined aberration is negative andof suicient amount to properly counteract Athe positive aberration of the element H.

When the element H is placed in juxtaposition to the element H, as shown in Fig. 1, it will be' seen that the point of emergence of the entire system (designated by h) lies be- 'tween the element H2 and the plane of the image, (designated by O.) When, however, the element H is moved along the optic axis by means of the mechanism described or other suitable means to the position shown in Fig.

2, it will be seen that the sum of the focal lengths of the elements H' and H2 will be approximately twice the focal length of the element H2, therebylengthening the equivalent focus of the entire system, and that the point of emergence in this instance will be situated between the two outer elements H and H2, the difference between the position of the point 7o h as shown in Fig; 1 and its position as shown in Fig. 2 being equal to the variation of the focal length of the entire system. By

so constructing the system that the negative element shall be of shorter focal length than either of the elements H and H2 it will be. seen that when the element H' is in j uxtaposition to the element H the point of emergence will be behind the element H2, and when the elements H and H2 are in juxtaposition the 8o point of emergence will be in front of the element H, thus making possible a greaterva- Vriation of the equivalent focal length of the system. Y In practice I prefer to use the form of lens system shown in Figs. 1 and 2. It is obvious, however, that the system may be transposed or differently arranged without the introduction of any new features. As an example,

Fig. 5 and Fig. 6 show an arrangement for the 9ov minimum and maximum focal length, respectively, of the same system as in Figs. l and 2 transposed, the element H3 being equal to the sum of the focal lengths of the elements H and H of Figs. 1 and 2, the element H4 being equal 95 as regards focal length to the element H' of Figs. 1 and 2, but of the positive or converging type, while the element H5 is equal to the sum of the focal lengths of the elements H' and H2. Fig. 7 and Fig. S'show another arroo rangement of the form shown in Figs. 1 and 2 when the element H in Figs. 1 and 2 is of shorter focal length than either of the elements H or H2. The element H6 is equal to thesum of the focal lengths of the elements H and H of Figs. 1 and 2. The element H7 is equal as regards focal length to the element H, but is positive, the element H8 being equal to the sum of the focal length of the elements H and H2. In the drawings the no elements H, H', H2, H6, and H2 are shown as single lenses. I do not desire to limit my. self to this form, however, as it is obvious that each element may bc composed of re than one lens. It will be seen that 1n order 'p to vary the magnitude of the image it will not be necessary to remove part or all of an objective, substituting therefor another part or objective having a different focal length, as is now the practice, as all that is necessary to I `2o be done with my invention is to move the central or intermedia-te `elementto the proper position between the two outer elements of` the system to produce any magnitude de'5 sired, from the smallest or minimum to the125 greatest or maximum magnitude.

As the center element is moved in one direction or the other it will be seen that its effects as regards each end element is dierent. For instance, in Figs. 1 and 2, when the 13o element H' is moved from the position shown in Fig. 1 to the position shown in Fig. 2, its

verging p ower of a convergingl lens or element being greater when the two are in contact and' decreasing'as their separation is increased.

Having thus described my invention, wh at I claimas new, and desire to `secure by Letters r 5 Patent, is-

An optical objective consisting of two xed outer lens elements, a movable intermediatey lens element adapted to be adjusted in varying intermediate positions between the two zo outer lens elements, and: means for adjusting Athe intermediate lens element, substantially 4as described.

CLILE C. ALLEN.

v Witnesses;

SAMUEL W. BANNINQ. THOMAS B. MOGREGOR. 

